Composite wood products, also known as engineered wood products, consist of wood-derived materials combined with other materials to form an aggregate material. An example is plywood, in which thin veneers of wood are joined together with adhesive to form a flat panel. Other examples of composite wood products include particle board, wafer board, gluelam beams, structural composite lumber, oriented strand board (OSB), and oriented strand lumber (OSL).
Composite wood products offer greater strength, reliability, and consistency compared to conventional lumber. Localized defects such as knots or density variations can be minimized or eliminated through the manufacturing process, giving a uniform product that is highly resistant to warping or splitting. More highly engineered products, such as OSB, typically perform within closer tolerances than less highly engineered products, such as plywood. Composite wood products use wood resources very efficiently because they may be manufactured from much smaller trees than conventional lumber, reducing the need to harvest “old growth” forests. About 85-90% of a log can be used to make high quality structural panels, and the remainder—bark, saw trim, and sawdust—can be converted into energy, pulp chips or bark dust.
However, one of the drawbacks of engineered products such as OSB is that it is often about 10-40% heavier than similarly-dimensioned plywood. The higher OSB weight is a concern among builders and other users of the products, especially where the product must be transported and handled by hand, such as on roofs. Consequently, a lighter weight OSB that maintains requisite strength performance is highly desirable.
Adding additives such as extenders or fillers into adhesive is a common practice in the manufacture of plywood. The purposes of adding filler or extender to an adhesive include increasing the initial viscosity, shortening the assembly time, preventing excessive penetration of adhesive into the wood, adding strength and reducing cost. However, conventional additives are not suitable for OSB and OSL production because of the method of applying adhesive. In plywood production, adhesive resin is applied to veneers by roller and sufficient adhesive is applied to form a continuous glue line. In contrast, in OSB and OSL production, the adhesive is typically atomized into fine resin drops (roughly 40-60 micrometers in diameter) as it is applied to the wood strands. Only a minimal amount of resin is used and a continuous glue line is not formed.
Thus, there is a need for a reinforced adhesive resin suitable for use in the production of lightweight OSB, OSL, and other engineered composite wood products.